Optical film and method of manufacturing the same

ABSTRACT

The present invention provides an optical film and a retardation film that each include an acryl resin, and 20 to 65 parts by weight of a graft copolymer including a conjugated diene rubber based on 100 parts by weight of the acryl resin, and an electronic device including the same.

TECHNICAL FIELD

The present invention relates to an optical film, and a method ofmanufacturing the same. More particularly, the present invention relatesto an optical film, in which the thermal stability and the toughness aresignificantly improved, and a method of manufacturing the same. Theoptical film can be usefully applied to an electronic device such asdisplay devices including LCDs. This application claims priority fromKorean Patent Application No. 10-2007-0094052 filed on Sep. 17, 2007 inthe Korean Intellectual Property Office, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND ART

In recent years, in accordance with the advance in optical technology,various types of display technologies such as plasma display panels(PDP), liquid crystal displays (LCD), organic/inorganic EL displays(ELD) and the like have been suggested and sold in the market instead ofa known cathode-ray tube. In the above-mentioned displays, the use ofvarious types of plastic films has been suggested and the requiredcharacteristics thereof have been sophisticated. For example, in thecase of the liquid crystal displays, in order to obtain the slimness andthe lightness and to improve display characteristics, various types ofplastic films are used in a polarizing plate, a retardation film, aplastic substrate, a light guide plate.

In the case of the polarizing plate, in general, the polarizing platehas a structure in which the triacetyl cellulose film (hereinafter,referred to as TAC film) acting as the protective film is laminated byusing the aqueous adhesive made of the polyvinyl alcohol aqueoussolution on the polarizer. However, both the polyvinyl alcohol film usedas the polarizer and the TAC film used as the protective film forpolarizers have poor heat resistance and humidity resistance. Therefore,if the polarizing plate that is made of the films is used at a hightemperature or a high humidity atmosphere for a long period of time, thedegree of polarization is reduced, the polarizer and the protective filmare separated from each other, or optical properties are reduced. Thus,in terms of the purposes, there are various limits. In addition, in thecase of the TAC film, a change in in-plane retardation (R_(in)) andthickness retardation (R_(th)) is significant according to a change inthe ambient temperature/humidity atmosphere. In particular, a change inretardation in respects to incident light at an inclined direction issignificant. If the polarizing plate that includes the TAC film havingthe above-mentioned characteristics as the protective film is applied toa liquid crystal display, the viewing angle characteristics are changedaccording to the change in the ambient temperature/humidity atmosphere,thus redwing the image quality. In addition, in the case of the TACfilm, a change in dimension is significant according to the change inthe ambient temperature/humidity atmosphere and the photoelasticcoefficient is relatively high, thus, after evaluation in respects todurability in a heat resistant and humidity resistant atmosphere, achange in retardation characteristic occurs locally, thereby easilyreducing the image quality.

As a material to complement the disadvantages of the TAC film, amethacryl resin is well known. However, it is known that the methacrylresin is easily broken or splited to cause problems in terms oftransportability during the production of the polarizing plate and theproductivity is poor. In addition, in the case of when the acrylateresin is used as the material of the film, since it is required that acasting process is used, there are problems in that it is difficult toperform the production process and the cost is high.

In the case of the retardation film, the film that is made of thestyrene resin is a material that shows the optical anisotropic propertythat the refractive index is increased perpendicular to the alignmentdirection when the film is stretched and aligned, and it is known thatthe film is stretched to be used for manufacturing the film having thepositive thickness retardation (R_(th)). In addition, there areadvantages in that the styrene resin has the excellent economicefficiency and transparency. However, there are problems in that theheat resistance is insufficient and the mechanical properties are poorexcept for the case of when the costly special monomer is used toperform the manufacturing. In addition, in the case of when thepolycarbonate resin is stretched to manufacture the retardation film, itis possible to provide the sufficient retardation function, but thechange in retardation is significant in respects to the degree ofstretching and it is difficult to provide the film having the uniformand stable retardation function.

DISCLOSURE OF INVENTION Technical Problem

The present invention has been made keeping in mind the problemsoccurring in the related art, and an object of the present invention isto provide an optical film that can be easily manufactured by using anextrusion process at low cost, and has the excellent heat resistance andtoughness, and a method of manufacturing the same. In the case of theoptical film, since the optical isotropic properties are excellentbefore the stretching the film can be used for various types of purposessuch as a polarizing plate protective film, and after the stretchingsince it is possible to provide the uniform and stable retardation, thefilm can be applied to a retardation film. It is another object of thepresent invention to provide a retardation film that is manufactured byusing the optical film and a method of manufacturing the same. It isstill another object of the present invention to provide an electronicdevice that includes the optical film or retardation film.

Technical Solution

The present invention provides an optical film that includes an acrylresin, and 20 to 65 parts by weight of a graft copolymer including aconjugated diene rubber based on 100 parts by weight of the acryl resin.

In addition, the present invention provides a method of manufacturing anoptical film, which includes a) preparing a resin composition thatincludes an acryl resin, and 20 to 65 parts by weight of a graftcopolymer including a conjugated diene rubber based on 100 parts byweight of the acryl resin, and b) forming a film by using the resincomposition.

In addition, the present invention provides a retardation film that ismanufactured by stretching the optical film.

In addition, the present invention provides a method of manufacturing aretardation film, which includes a) preparing a resin composition thatincludes an acryl resin, and 20 to 65 parts by weight of a graftcopolymer including a conjugated diene rubber component based on 100parts by weight of the acryl resin, b) forming a film by using the resincomposition, and c) uniaxially or biaxially stretching the film.

In addition, the present invention provides an electronic device thatincludes the optical film or retardation film.

ADVANTAGEOUS EFFECTS

An optical film according to the present invention has the excellentheat resistance and toughness. Since the optical isotropic propertiesare excellent before the stretching the film can be used for varioustypes of purposes such as a polarizing plate protective film, thusreplacing a known costly TAC resin. After the stretching since it ispossible to provide the uniform and stable retardation, the film can beapplied to a retardation film. In addition, since the optical filmaccording to the present invention can be manufactured by using anextrusion process, the manufacturing method can be easily performed andthe manufacturing cost is low. Accordingly, the film according to thepresent invention has the effect that is better than that of a knownfilm that is made of only the acrylate resin.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.

An optical film according to the present invention includes an acrylresin and a graft copolymer that includes a conjugated diene rubbercomponent.

Since it is required that a film material used in image display devicessuch as LCDs has high stability and heat resistance to ultraviolet rays,it is known that a conjugated diene compound having a double bond is notused. Accordingly, as the film material used for the purpose requiringheat resistance of image display devices such as LCDs and the like, anexample in which an impact redwing substance including the conjugateddiene rubber is used in a large amount of 20 to 65 parts by weight basedon 100 parts by weight of an acryl resin that is a matrix resin is notknown. However, the present inventors have found that in the case ofwhen the conjugated diene rubber component is used as a copolymer havinga predetermined structure, when a component and a component ratio of thecopolymer are controlled, the toughness of the film is improvedaccording to the conjugated diene compound, and the reduction instability and heat resistance that are known as problems of the knownconjugated diene compound can be avoided.

In the present invention, the graft copolymer includes the conjugateddiene rubber component in an amount of 20 to 65 parts by weight based on100 parts by weight of the acryl resin that acts as a matrix. In thecase of when the graft copolymer is included in an amount of less than20 parts by weight, the toughness of the optical film is reduced, and inthe case of when the amount is more than 65 parts by weight, there areproblems in that it is difficult to process the film, the haze of thefilm is increased, and the glass transition temperature is reduced.

In the present invention, it is preferable that the graft copolymerincluding the conjugated diene rubber is the graft copolymer of aconjugated diene rubber component and an acryl resin. The type of thegraft copolymer is not limited, but it is preferable that the graftcopolymer have a core-shell structure in which the conjugated dienerubber component constitutes a core and an acryl resin constitutes ashell.

In the graft copolymer, a weight ratio of the conjugated diene rubbercomponent and the acryl resin is in the range of preferably 10 to 50:90to 50, and more preferably 15 to 45:85 to 55. In the graft copolymer, inthe case of when the weight ratio of the conjugated diene rubbercomponent is less than 10% by weight, there is a problem in that thetoughness of the optical film is not sufficient. In the case of when theweight ratio is more than 50% by weight, the dispersibility is reducedto rapidly increase the haze and the thermal expansion coefficient andreduce the glass transition temperature.

Among the graft copolymers, examples of the conjugated diene rubbercomponent are not limited, but may include a butadiene copolymer such asan ethylene-propylene diene rubber, a butadiene rubber, astyrene-butadiene rubber and the like, and it is more preferable to usethe butadiene rubber.

Among the graft copolymers, examples of the acryl resin are not limited,but may include a homo or copolymer of the acryl monomer; a copolymer ofan acryl monomer and an aromatic vinyl monomer; a copolymer of an acrylmonomer, an aromatic vinyl monomer and an acrylonitrile monomer; acopolymer of an acryl monomer, an aromatic vinyl monomer and an acidanhydride; a copolymer of an acryl monomer, an aromatic vinyl monomer,an acrylonitrile monomer and an acid anhydride and the like.

A compound which has a double bond between a carbonyl group of an estergroup and conjugated carbons may be used as the acryl monomer, andexamples of a substituent group thereof is not limited. The acrylmonomer that is described in the present specification includes acrylateand an acrylate derivative, and is a notion including alkyl acrylate,alkyl methacrylate, alkyl butacrylate and the like. For example,examples of the acryl monomer include a compound that is represented bythe following Formula 1.

wherein R₁, R₂ and R₃ are each independently a hydrogen atom, or amonovalent hydrocarbon group that includes or not a hetero atom and has1 to 30 carbon atoms, at least one of R₁, R₂ and R₃ may be an epoxygroup, and R₄ is a hydrogen atom or an alkyl group having 1 to 6 carbonatoms.

Specific examples of the acryl monomer may include one or more acrylmonomers selected from the group consisting of methyl acrylate, ethylacrylate, methyl methacrylate, ethyl methacrylate, methyl ethacrylate,and ethyl ethacrylate, and in particular, it is most preferable to usemethyl methacrylate (MMA).

It is preferable that a monomer having a structure in which a benzenenucleus is substituted or unsubstituted with one or more C₁ to C₅ alkylgroups or halogen groups be used as the aromatic vinyl monomer. Forexample, it is preferable that one or more styrene monomers selectedfrom the group consisting of styrene or α-methyl styrene be used.

Preferable examples of the acrylonitrile monomer include one or moreacrylonitrile monomers selected from the group consisting ofacrylonitrile, methaacrylonitrile, and ethaacrylonitrile.

The carboxylic acid anhydride may be used as the acid anhydride, andmonovalent or polyvalent carboxylic acid anhydride including divalentcarboxylic acid anhydride may be used. Preferably, maleic acid anhydrideor a derivative thereof may be used, and for example, a compound that isrepresented by the following Formula 2 may be used.

wherein R₇ and R₈ are each independently hydrogen atom or an alkyl grouphaving 1 to 6 carbon atoms.

In the present invention, among the graft copolymers, in the case ofwhen a copolymer of the acryl monomer, the aromatic vinyl monomer, andthe acrylonitrile monomer, or a copolymer of the acryl monomer, thearomatic vinyl monomer and the acid anhydride as the acryl resin, ispreferable that the weight ratio be in the range of 55 to 80:10 to 35:4to 15.

The conjugated diene rubber component and the acryl resin may besubjected to graft polymerization by using a method that is known in theart, and for example, a general emulsification polymerization method maybe used. It is preferable that the graft ratio be in the range of 30 to60%. The particle size of the core including the conjugated diene rubbercomponent is in the range of preferably 150 to 400 nm and morepreferably 200 to 300 nm, but the scope of the present invention is notlimited thereto.

In the present invention, a substance that is known in the art may beused as the acryl resin that acts as the matrix of the optical film. Inparticular, it is preferable to use a homo or copolymer of the acrylmonomer; a copolymer of the acryl monomer and the aromatic vinylmonomer; a copolymer of the acryl monomer, the aromatic vinyl monomerand the acrylonitrile monomer; a copolymer of the acryl monomer, thearomatic vinyl monomer and the acid anhydride; or a copolymer of theacryl monomer, the aromatic vinyl monomer, the acrylonitrile monomer andthe acid anhydride. It is more preferable to use the copolymer of theacryl monomer, the aromatic vinyl monomer and the acrylonitrile monomer;the copolymer of the acryl monomer, the aromatic vinyl monomer and theacid anhydride; or the copolymer of the acryl monomer, the aromaticvinyl monomer, the acrylonitrile monomer and the acid anhydride.

In the case of when the copolymer of the acryl monomer, the aromaticvinyl monomer and the acrylonitrile monomer or the copolymer of theacryl monomer, the aromatic vinyl monomer and the acid anhydride is usedas the matrix resin, it is preferable that the weight ratio of each ofthe monomers be in the range of 55 to 80:10 to 35:4 to 15. Examples ofthe monomers are the same as those of the components that are describedin respects to the acryl resin among the graft copolymers. The acrylmonomer may contribute to optical properties, the aromatic vinyl monomermay contribute to the formability and the retardation provision of thefilm, and the acrylonitrile monomer and the acid anhydride maycontribute to the heat resistance. The matrix resin may be polymerizedby using the method that is known in the art, and for example, the bulkpolymerization method may be used.

The copolymer that constitutes the acryl resin acting as the matrix mayfurther include one or more monomers selected from the (meth)acrylicacid and imide monomers as an additional comonomer. The acrylic acid andmethacrylic acid or a derivative thereof may be used as the(meth)acrylic acid. The phenyl maleimide, cyclohexyl maleimide and thelike may be used as the imide monomer. In the case of when the(meth)acrylic acid and imide monomers are included, it is preferablethat the amount be 15 parts by weight or less based on 100 parts byweight of the copolymer.

The above-mentioned matrix resin is characterized in that the glasstransition temperature is in the range of 120 to 130° C., the molecularweight is in the range of 120000 to 150000, the MI (220° C., 10 kg) is10 or less, and preferably 4 to 10, and the haze is in the range of 0.1to 2%. The MI is an index that illustrates the flow of the resin andmeans an amount of the resin per minute when a load of 10 kg is appliedat 220° C. In addition, the matrix resin has the refractive index in therange of preferably 1.48 to 1.545 and more preferably 1.485 to 1.535 inorder to obtain the transparency required in the optical film.

The optical film according to the present invention may be manufacturedby forming a film using the resin composition including the graftcopolymer and the acryl resin.

The method of forming the film may be performed by using a method thatis known in the art. The optical film according to the present inventionmay be manufactured by an extrusion process in addition to a castingprocess unlike the film that is made of the acryl resin.

In order to manufacture the optical film, a general additive, forexample, a plasticizer, a lubricant, an impact buffering material, astabilizing agent, a ultraviolet ray absorption agent and the like, maybe added to the resin composition. In particular, in the case of whenthe optical film according to the present invention is used as aprotective film of a polarizer, in order to protect the polarizer andthe liquid crystal panel from the external ultraviolet rays, it ispreferable to add the ultraviolet ray absorbing agent to the resincomposition. Examples of ultraviolet ray absorbing agent may include,but are not limited to a benzotriazole ultraviolet ray absorbing agentand a triazine ultraviolet ray absorbing agent, and a hindered aminelight stabilizer such as bis(2,2,6,6-tetramethyl-4-piperidyl) sebaceatemay be used. Preferably, Tinuvin328, Tinuvin321 and Tinuvin 360 may beused. Igafos 168, Iganox 1076, and Iganox 245 may be added as thethermal stabilizing agent.

The thickness of the optical film according to the present invention maybe in the range of 20 to 200 μm, and preferably 40 to 120 μm. In theoptical film according to the present invention, a glass transitiontemperature is in the range of 110 to 130° C., a thermal deformationtemperature (Vicat) is in the range of 110 to 140° C., an MI (220° C.,10 kg) is in the range of 2 to 6, and the toughness is excellent. Inaddition, the case of the optical film according to the presentinvention, preferably, a thermal expansion coefficient CTE (ppm/K, 40 to90° C.) is in the range of 50 to 120, a haze is in the range of 0.5 to3%, and a transmittance is in the range of 88 to 93%.

In the optical film according to the present invention, an in-planeretardation value and a thickness retardation value may be in the rangeof 0 to 10 nm before the stretching and in the case of when the film isuniaxially or biaxially stretched, the in-plane retardation value andthe thickness retardation value may be in the range of 80 to 200 nm.

The stretching process of the optical isotropic film is performed at atemperature range of preferably Tg−30° C. to Tg+30° C. and morepreferably Tg−10° C. to Tg+20° C. based on the glass transitiontemperature (Tg) of the resin composition. In addition, the stretchingspeed and the stretching ratio may be appropriately controlled in therange capable of achieving the object of the present invention.

The optical film according to the present invention may be used as apolarizer protective film. In this case, the surface may be reformed inorder to improve the adhesion strength. Examples of the reforming methodinclude a method of treating a surface of the protective film by usingcorona treatment, plasma treatment, and UV treatment, and a method offorming a primer layer on the surface of the protective film. Both themethods may be used simultaneously. The type of the primer is notlimited, but it is preferable to use the compound having the reactivefunctional group such as a silnae coupling agent.

The polarizing plate that includes the optical film according to thepresent invention as the protective film includes a polarizer and aprotective film provided on at least one side of the polarizer, and atleast one of the protective films may have a structure that is theoptical film according to the present invention.

In the present invention, any polarizer may be used as long as thepolarizer is known in the art, and for example, a film which containsiodine or dichromatic dyes and is made of polyvinyl alcohol (PVA) may beused. The polarizer may be produced by applying iodine or dichromaticdyes on the PVA film. However, the production method of the polarizingplate is not limited. In the specification, the polarizer does notinclude the protective film, and the polarizing plate includes thepolarizer and the protective film.

The adhesion of the polarizer and the protective film may be performedby using an adhesive layer. Examples of the adhesive which is capable ofbeing used to combine the protective film and the polarizing plate arenot limited as long as the adhesive is known in the art. Examples of theadhesive include, but are not limited to a one- or two-liquid typepolyvinyl alcohol (PVA) adhesive, a polyurethane adhesive, an epoxyadhesive, a styrene-butadiene rubber (SBR) adhesive, a hot melt adhesiveand the like.

Among the adhesives, it is preferable to use a polyvinyl alcoholadhesive. In particular, it is preferable to use the adhesive thatincludes the polyvinyl alcohol resin having the acetacetyl group and theamine metal compound crosslinking agent. The adhesive for the polarizingplate may include 100 parts by weight of the polyvinyl alcohol resinhaving the acetacetyl group and the 1 to 50 parts by weight of the aminemetal compound crosslinking agent.

The polyvinyl alcohol resin is not limited as long as the resin iscapable of desirably attaching the polarizer and the protective film toeach other, and has excellent optical penetration and no consecutivechange such as yellowing. In consideration of the desirable crosslinkingreaction to the crosslinking agent, it is preferable to use thepolyvinyl alcohol resin containing the acetacetyl group.

The degree of polymerization and saponification of the polyvinyl alcoholresin are not limited as long as the polyvinyl alcohol resin containsthe acetacetyl group, but it is preferable that the degree ofpolymerization be 200 to 4,000 and the degree of saponification be 70 to99.9 mol %. In consideration of the desirable mixing to the containedmaterial according to the free movement of molecules, it is morepreferable that the degree of polymerization is 1,500 to 2,500 and thedegree of saponification is 90 to 99.9 mol %. In connection with this,it is preferable that the polyvinyl alcohol resin contain 0.1 to 30 mol% of acetacetyl group. In the above-mentioned range, the reaction to thecrosslinking agent may be desirably performed and the adhesive may havethe desired waterproofing property and adhesion strength.

The amine metal compound crosslinking agent is a water-solublecrosslinking agent that contains a functional group having a reactivityto the polyvinyl alcohol resin, and preferably, a metal complexcontaining an amine ligand. Examples of metal that is capable of beingapplied to the metal complex include a transition metal such aszirconium (Zr), titanium (Ti), hafnium (Hf), tungsten (W), iron (Fe),cobalt (Co), nickel (Ni), ruthenium (Ru), osmium (Os), rhodium (Rh),iridium (Ir), palladium (Pd), and platinum (Pt). Examples of the ligandthat is coupled with the central metal may include any ligand as long asthe ligand contains at least one amine group such as primary amines,secondary amines (diamines), tertiary amines, or ammonium hydroxides. Itis preferable that the amount of the crosslinking agent be 1 to 50 partsby weight based on 100 parts by weight of polyvinyl alcohol resin. Inthe above-mentioned range, it is possible to provide significantadhesion strength to the target adhesive and to improve the storagestability (pot life) of the adhesive.

It is preferable that the pH of the adhesive aqueous solution includingthe polyvinyl alcohol resin containing the acetacetyl group and theamine metal compound crosslinking agent be controlled to 9 or less usinga pH controlling agent. More preferably, the pH may be controlled tomore than 2 and 9 or less, and even more preferably, 4 to 8.5.

The combination of the polarizer and the protective film may beperformed according to an attachment method using an adhesive. That is,the adhesive is applied on the surface of the PVA film that is theprotective film of the polarizer or the polarizer by using a roll water,a gravure water, a bar water, a knife water, a capillary water, or thelike. Before the adhesive is completely dried, the protective film andthe polarizing film are combined with each other using heat pressing orpressing at normal temperature by means of a combination roll. When ahot melt type adhesive is used, the heat pressing roll is used.

If the polyurethane adhesive is to be used, it is preferable to use thepolyurethane adhesive produced by using an aliphatic isocyanate compoundwhich does not cause yellowing due to light. If an one- or two-liquidtype dry laminate adhesive or an adhesive having relatively lowreactivity in respects to isocyanate and a hydroxy group is used, asolution type adhesive which is diluted with an acetate solvent, aketone solvent, an ether solvent, or an aromatic solvent may be used. Inthis connection, it is preferable that the adhesive have low viscosityof 5000 cps or less. Preferably, the adhesive has excellent storagestability and light transmittance of 90% or more at a wavelength of 400to 800 nm.

If showing sufficient tackifying power, a tackifier may be used for thelamination of the protective film and the polarizing film. If used, atackifier is preferably heat- or UV-cure sufficiently to show resultingmechanical strength as high as that obtained with an adhesive. Also, theinterface adhesion of the tackifier useful in the present invention islarge enough so that delamination is possible only when one of the filmsbonded to each other therethrough is destroyed.

Specific examples of the tackifier may include natural rubber, syntheticrubber, or elastomer, a vinyl chloride/vinyl acetate copolymer,polyvinyl alkyl ether, poly-acrylate, modified polyolefin adhesivehaving excellent optical transparency, and a curable tackifiercontaining a curing agent such as isocyanate.

The manufactured polarizing plate may be used for the various purposes.Specifically, the polarizing plate may be preferably applied to an imagedisplay device such as a polarizing plate for liquid crystal displays(LCD) and a polarizing plate for preventing the reflection of theorganic EL display device. In addition, the optical film according tothe present invention may be applied to a complex polarizing plate inwhich various optical layers such as various types of functional layers,for example, a retardation plate such as a λ/4 plate and a λ/2 plate, anoptical diffusion plate, a viewing angle enlargement plate, a luminanceimprovement plate, and a reflection plate are combined with each other.

The polarizing plate may include an tackifier layer on at least one sidethereof so as to be easily applied to image display devices and thelike. In addition, the polarizing plate may further include a releasefilm on the tackifier layer in order to protect the tackifier layeruntil the polarizing plate is applied to an image display device.

In addition, the present invention provides an electronic device thatincludes the optical film or the retardation film. The electronic devicemay be an image display device such as LCDs. For example, the presentinvention provides an image display device that includes a light source,a first polarizing plate, a liquid crystal cell, and a second polarizingplate sequentially layered, and also includes the optical film or theretardation film according to the present invention as at least oneprotective film of the first polarizing plate and the second polarizingplate or the retardation film that is provided between at least one ofthe first polarizing plate and the second polarizing plate and theliquid crystal cell.

The liquid crystal cell includes a liquid crystal layer; a substratethat is capable of supporting the liquid crystal layer; and an electrodelayer to apply voltage to the liquid crystal. At this time, the opticalfilm or the retardation film according to the present invention may beapplied to a liquid crystal mode such as an In-Plane Switching mode (IPSmode), a Vertically Aligned mode (VA mode), an OCB mode (OpticallyCompensated Birefringence mode), a Twisted Nematic mode (TN mode), and aFringe Field Switching mode (FFS mode).

MODE FOR THE INVENTION

A better understanding of the present invention may be obtained in lightof the following Examples which are set forth to illustrate, but are notto be construed to limit the present invention.

Example 1

The resin composition that included 80% by weight of the matrix resin inwhich the ratio of SM-MMA-MAH (styrene-methyl methacrylate-maleicanhydride) was 23:70:7% by weight and the weight average molecularweight was 130000, and 20% by weight of the impact buffering materialthat had the molecular weight of 130000 except for the rubber and theratio of the core (butadiene rubber) and shell (SM-MMA-AN=25:70:5) thatwas 25:75 was subjected to dry blending to manufacture the heatresistant blend of pellet state by using the unidirectional two-axisextrusion device. After the manufactured pellet was dried, the extrudedfilm having the thickness of 80 μm was manufactured by using theextrusion device including the T-die. The physical properties of themanufactured film were measured, and the results are described in thefollowing Table 1.

Example 2

The physical properties of the film were measured by using the samemethod as that of Example 1, except that the resin composition thatincluded 75% by weight of the matrix resin in which the ratio ofSM-MMA-MAH (styrene-methyl methacrylate-maleic anhydride) was 23:70:7%by weight and the weight average molecular weight was 130000, and 25% byweight of the impact buffering material that had the molecular weight of130000 except for the rubber and the ratio of the core and shell thatwas 25:75 was used, and the results are described in the following Table1.

Example 3

The physical properties of the film were measured by using the samemethod as that of Example 1, except that the resin composition thatincluded 80% by weight of the matrix resin in which the ratio ofSM-MMA-MAH (styrene-methyl methacrylate-maleic anhydride) was 23:70:7%by weight and the weight average molecular weight was 130000, and 20% byweight of the impact buffering material that had the molecular weight of130000 except for the rubber and the ratio of the core and shell thatwas 30:70 was used, and the results are described in the following Table1.

Example 4

The physical properties of the film were measured by using the samemethod as that of Example 1, except that the resin composition thatincluded 75% by weight of the matrix resin in which the ratio ofSM-MMA-MAH (styrene-methyl methacrylate-maleic anhydride) was 23:67:10%by weight and the weight average molecular weight was 130000, and 25% byweight of the impact buffering material that had the molecular weight of130000 except for the rubber and the ratio of the core and shell thatwas 30:70 was used, and the results are described in the following Table1.

Example 5

The physical properties of the film were measured by using the samemethod as that of Example 1, except that the resin composition thatincluded 80% by weight of the matrix resin in which the ratio ofSM-MMA-MAH (styrene-methyl methacrylate-maleic anhydride-acrylonitrile)was 23:65:7:5% by weight and the weight average molecular weight was130000, and 20% by weight of the impact buffering material that had themolecular weight of 130000 except for the rubber and the ratio of thecore and shell that was 30:70 was used, and the results are described inthe following Table 1.

Example 6

The physical properties of the film were measured by using the samemethod as that of Example 1, except that the resin composition thatincluded 70% by weight of the matrix resin in which the ratio ofSM-MMA-CHMI (styrene-methyl methacrylate-cyclohexylmaleimide) was23:70:7% by weight and the weight average molecular weight was 130000,and 30% by weight of the impact buffering material that had themolecular weight of 130000 except for the rubber and the ratio of thecore and shell that was 20:80 was used, and the results are described inthe following Table 1.

Example 7

The physical properties of the film were measured by using the samemethod as that of Example 1, except that the resin composition thatincluded 80% by weight of the matrix resin in which the ratio ofSM-MMA-MAH (styrene-methylmethacrylate-maleic anhydride) was 23:70:7% byweight and the weight average molecular weight was 130000, and 20% byweight of the impact buffering material that had the molecular weight of130000 except for the rubber and the ratio of the core and shell thatwas 40:60 was used, and the results are described in the following Table1.

Example 8

The physical properties of the film were measured by using the samemethod as that of Example 1, except that the resin composition thatincluded 80% by weight of the matrix resin in which the ratio ofSM-MMA-MAH (styrene-methylmethacrylate-maleic anhydride) was 23:70:7% byweight and the weight average molecular weight was 130000, and 20% byweight of the impact buffering material that had the molecular weight of130000 except for the rubber and the ratio of the core and shell thatwas 50:50 was used, and the results are described in the following Table1.

Comparative Example 1

The physical properties of the film were measured by using the samemethod as that of Example 1, except that the resin composition thatincluded 90% by weight of the matrix resin in which the ratio ofSM-MMA-MAH (styrene-methylmethacrylate-maleic anhydride) was 23:70:7% byweight and the weight average molecular weight was 130000, and 10% byweight of the impact buffering material that had the molecular weight of130000 except for the rubber and the ratio of the core and shell thatwas 30:70 was used, and the results are described in the following Table2.

Comparative Example 2

The physical properties of the film were measured by using the samemethod as that of Example 1, except that the resin composition thatincluded 60% by weight of the matrix resin in which the ratio ofSM-MMA-MAH (styrene-methylmethacrylate-maleic anhydride) was 23:70:7% byweight and the weight average molecular weight was 130000, and 40% byweight of the impact buffering material that had the molecular weight of130000 except for the rubber and the ratio of the core and shell thatwas 30:70 was used, and the results are described in the following Table2.

Comparative Example 3

The physical properties of the unstretched TAC film (thickness 80 μm,Fuji film) were measured by using the same method as Example 1, and theresults are described in the following Table 2.

TABLE 1 Example No. 1 2 3 4 5 6 7 8 Tg (° C.) 120 119 118 125 116 117115 118 Haze (%) 0.9 1.2 1.1 1.5 1.1 1.3 1.6 2.3 Toughness ◯ ◯ ◯ ◯ ◯ ◯ ◯◯ Straight 92 91 90 90 90 91 89 88 transmittance (%) Retardation R_(in)1 1 1 1 1 1 1 1 before stretching R_(th) 7 8 7 9 9 7 9 8 RetardationR_(in) 150 148 150 150 165 130 120 100 after stretching R_(th) 150 150150 150 170 130 120 110 Thermal expansion 82 89 86 100 85 90 110 150coefficient (CTE)

TABLE 2 Comparative Example No. 1 2 3 Tg (° C.) 123 107 130 Haze (%) 0.72.8 0.3 Toughness X ◯ ◯ Straight transmittance (%) 93 87 92 Retardationbefore R_(in) 1 1 1 stretching R_(th) 7 8 −50 Retardation after R_(in)120 120 stretching R_(th) 150 121 Thermal expansion 79 160 40coefficient (CTE)

(1) Measurement of the haze and the straight transmissivity—Themeasurement was performed by using the ASTM 1003 method.

(2) Toughness—The measurement was performed by folding using hands thefilm having the thickness of 80 μm ten times to check the breaking (◯:No breaking Δ: the breaking occurs one to three times, and X: thebreaking occurs four or more times).

(3) Tg (glass transition temperature)—The measurement was performed byusing Pyris 6 DSC (Differential Scanning Calorimeter) that wasmanufactured by Perkin Elmer, Inc.

(4) Retardation—The refractive index was measured by using the Abberefractometer and the calculation was performed by using thesample-gradient type automatic double refraction device according to thefollowing Equations.

R _(in) =d×(n _(x) −n _(y))

R _(th) =d×(n _(z) −n _(y))

(wherein, d is the thickness of the film, n_(x) is the x-axis directionrefractive index of the in-plane refractive index, n_(y) is the y-axisdirection refractive index of the in-plane refractive index, and n_(z)is the thickness direction refractive index)

(5) Thermal expansion coefficient (CTE)—The measurement was performedwhile the temperature of the film was increased by using the DMA device.

As shown in Table 1, the optical films that were manufactured inExamples 1 to 8 had the excellent toughness and the glass transitiontemperature of 115° C. or more, and the glass transition temperature wasnot reduced. In addition, the optical films that were manufactured inExamples 1 to 8 had the excellent optical isotropic property before thestretching and the uniform and stable retardation was obtained after thestretching. On the other hand, as shown in Table 2, in ComparativeExample 1 in which the graft copolymer including the conjugated dienerubber is used in a small amount, it was impossible to obtain thesufficient toughness. In addition, there were problems in that inComparative Example 2 in which the graft copolymer including theconjugated diene rubber is used in an excessive amount, the haze wassignificantly increased and the glass transition temperature wassignificantly reduced.

1. An optical film comprising: an acryl resin; and 20 to 65 parts byweight of a graft copolymer comprising a conjugated diene rubber basedon 100 parts by weight of the acryl resin.
 2. The optical film as setforth in claim 1, wherein a glass transition temperature is in the rangeof 110 to 130° C., a thermal deformation temperature (Vicat) is in therange of 110 to 140° C., an MI (220° C., 10 kg) is in the range of 2 to6, a thermal expansion coefficient CTE (ppm/K, 40 to 90° C.) is in therange of 50 to 120, a haze is in the range of 0.5 to 3%, and atransmittance is in the range of 88 to 93%.
 3. The optical film as setforth in claim 1, wherein an in-plane retardation value and a thicknessretardation value are in the range of 0 to 10 nm.
 4. The optical film asset forth in claim 1, wherein the acryl resin comprises one or moreselected from the group consisting of a copolymer of an acryl monomer,an aromatic vinyl monomer and an acrylonitrile monomer; a copolymer ofan acryl monomer, an aromatic vinyl monomer and an acid anhydride; and acopolymer of an acryl monomer, an aromatic vinyl monomer, anacrylonitrile monomer and an acid anhydride.
 5. The optical film as setforth in claim 4, wherein the copolymer that is selected from the groupconsisting of the copolymer of the acryl monomer, the aromatic vinylmonomer and the acrylonitrile monomer; the copolymer of the acrylmonomer, the aromatic vinyl monomer and the acid anhydride; and thecopolymer of the acryl monomer, the aromatic vinyl monomer, theacrylonitrile monomer and the acid anhydride is a copolymer thatcomprises one or more monomers of (meth)acrylic acid and imide monomersas an additional comonomer.
 6. The optical film as set forth in claim 1,wherein the conjugated diene rubber comprises one or more selected fromthe group consisting of an ethylene-propylene diene rubber, a butadienerubber and a styrene-butadiene rubber.
 7. The optical film as set forthin claim 1, wherein the graft copolymer is a graft copolymer of aconjugated diene rubber and an acryl resin.
 8. The optical film as setforth in claim 7, wherein a weight ratio of the conjugated diene rubberand the acryl resin of the graft copolymer is in the range of 10 to50:90 to
 50. 9. The optical film as set forth in claim 7, wherein thegraft copolymer has a core-shell structure in which the conjugated dienerubber constitutes a core and the acryl resin constitutes a shell. 10.The optical film as set forth in claim 9, wherein a weight ratio of theconjugated diene rubber and the acryl resin of the graft copolymer is inthe range of 10 to 50:90 to
 50. 11. The optical film as set forth inclaim 7, wherein the acryl resin of the graft copolymer comprises one ormore selected from the group consisting of a homo or copolymer of theacryl monomer; a copolymer of an acryl monomer and an aromatic vinylmonomer; a copolymer of an acryl monomer, an aromatic vinyl monomer andan acrylonitrile monomer; a copolymer of an acryl monomer, an aromaticvinyl monomer and an acid anhydride; and a copolymer of an acrylmonomer, an aromatic vinyl monomer, an acrylonitrile monomer and an acidanhydride.
 12. A method of manufacturing an optical film, the methodcomprising: a) preparing a resin composition that comprises an acrylresin, and 20 to 65 parts by weight of a graft copolymer comprising aconjugated diene rubber component based on 100 parts by weight of theacryl resin; and b) forming a film by using the resin composition.
 13. Aretardation film that is manufactured by stretching the optical filmaccording to claim
 1. 14. The retardation film as set forth in claim 13,wherein an in-plane retardation value and a thickness retardation valueare in the range of 80 to 200 nm.
 15. A method of manufacturing aretardation film, the method comprising: a) preparing a resincomposition that comprises an acryl resin, and 20 to 65 parts by weightof a graft copolymer comprising a conjugated diene rubber componentbased on 100 parts by weight of the acryl resin; b) forming a film byusing the resin composition; and c) uniaxially or biaxially stretchingthe film.
 16. A polarizing plate comprising: a polarizer; and protectivefilms that are provided at least one side of the polarizer, wherein atleast one of the protective films is the optical film according toclaim
 1. 17. An electronic device comprising: the optical film accordingto claim
 1. 18. An electronic device comprising: the retardation filmaccording to claim
 13. 19. An electronic device comprising: thepolarizing plate according to claim 16.